My U.S. Pat. Nos. 3,716,267 and 4,015,375 disclose unified floor frame assemblies for constructing a building. In the latter of the two patents mentioned above there is disclosed, as components of the floor frame structure, a floor joist formed of wood which is spaced along dual, parallel, steel I-beams. Because of newly applied and proposed Federal code requirements for mobile buildings, the floor joists were spaced relatively closely. While code requirements were met by the earlier structure, the relatively large number of joist assemblies required in the structure add substantially to the cost of the building.
The present application discloses an improved floor joist assembly for use in a floor frame assembly such as that disclosed in my U.S. Pat. No. 4,015,375. It is formed by both wood and steel components but these are arranged so that the steel portion provides improved rigidity and load bearing capacity. The wooden components are mounted so that they face outwardly around the perimeter of the joist assembly and thus provide wood surfaces for nailing, stapling or the like. Application of the flooring, insulation and bottom board or covering can thus proceed using conventional nailing or power-stapling techniques. This can occur even though the core of the assembly is formed of steel (channel) structural members.
The result is that the joist assemblies may be more widely spaced (a distance of the order of 48 inches) while conventional two by four lumber may be used at, for example, 16 inch spacing between the joist assemblies. The number of joist assemblies necessary for a given structure to meet code requirements is thus reduced as, correspondingly, is the over-all cost of the building. After completion of the installation of the floor components (both floor and bottom board components) the steel components of the joist assembly are enclosed within the floor structure eliminating the necessity for, and cost of, painting the steel. Moisture and rusting problems, over the long term, are minimized thereby reducing maintenance by the owner of the mobile building.